"Tattoo" by Hilary Duff
Not only did Sheeran write the song for Duff, but he also helped her record it . . . at midnight. She told MTV News, "He had been doing a promo day in L.A. and he's like, 'I know you have a 2-year-old, but could you please come and record at midnight?' . . . He vocally produced it and came in the booth with me. I was really intimidated because, normally, they don't do that, so I kept looking up and being like, 'You're Ed Sheeran and I'm singing the song that you wrote and I want to do right by it' . . . It was awesome and then he, in like 15 minutes, did all the low stuff and the harmonies and the background. He just musically has to put in no effort it seems; it's just him."